1. Field of the Invention
This invention relates to a new silacyclohexane compound, a method of preparing it, and a liquid crystal composition which contains it, as well as a liquid crystal display element which contains said liquid crystal composition.
2. The Prior Art
A liquid crystal display element utilizes the optical anisotropy and dielectric anisotropy of liquid crystal substances. Display methods include the TN mode (twisted nematic mode), the STN mode (super twisted nematic mode), the SBE mode (super birefringence mode), the DS mode (dynamic scattering mode), the guest-host mode, the DAP mode ("deformation of aligned phase" mode) and the OMI mode (optical mode interference mode). The most common display device has a twisted nematic structure based on the Schadt-Helfrich mode.
The properties required of the liquid crystal substance used in these liquid crystal displays are somewhat different depending on the display method. However, a wide liquid crystal temperature range and stability with regard to moisture, air, light, heat, electric fields, etc., are properties commonly required in all display methods. Furthermore, it is desirable for the liquid crystal material to have a low viscosity, and also to have a short address time, low threshold voltage and high contrast in the cell(s).
Currently, there is no single compound which satisfies all these requirements. In practice, liquid crystal mixtures are obtained by mixing several to more than ten liquid crystal compounds and latent liquid crystal compounds. Because of this, it is also important that components of a liquid crystal composition mix easily.
Among liquid crystal compounds which can be components for these, one of the basic components conventionally known which controls the electro-optical performance is a compound which has a so-called cyclohexyl ring-ethylene-phenyl ring-phenyl ring structure (BECH structure) such as those shown below. ##STR3## (See Japanese examined patent publication Tokko Sho 59-35900.) ##STR4## (See Japanese examined patent publication Tokko Sho 59-35900.) ##STR5## (See Japanese examined patent publication Tokko Hei 3-22855.) ##STR6## (See Japanese unexamined patent publication Tokkai Hei 2-233626.)
In recent years, along with the expansion of the applications of liquid crystal displays, the characteristics required of liquid crystal materials are becoming more and more advanced and demanding. In particular, superior characteristics such as improved low temperature performance, a wider temperature range for automobile onboard use and a lower driving voltage, compared with conventional liquid crystal substances, are desired.